Using rice water for orchids is one of those do-it-yourself tips that have been passed down for generations. But when someone asks what’s in rice water or how it helps orchids grow, no one has a concrete answer. So we set out to find out, and just like the article on garlic water , we were pleasantly surprised by the results.
Rice water is good for orchids because it:
- is rich in starch, which is attractive to beneficial fungi in the orchid soil
- provides the orchid with protein, free amino acids, calcium, phosphorus, iron, zinc, potassium, thiamine, riboflavin and niacin
- promotes the growth of healthy orchid leaves and stronger, larger orchid roots.
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The NPK ratio of rice water and its effect on orchids.
Rice water contains mainly rice particles, but also other minerals added to the rice plantation. Half of the water-soluble minerals are transferred from the rice to the water. In a study by Malakar and Banarjee (1959), it was reported that after rice was rinsed, the nutrients it transferred to the water were approximately: 7% protein, 30% crude fiber, 15% free amino acids, 25% calcium (Ca), 47% phosphorus (P), 47% iron (Fe), 11% zinc (Zn), 41% potassium (K), 59% thiamine, 26% riboflavin, and 60% niacin.
The authors justify the lack of an exact NPK ratio by saying that it depends on what rice you use, how much water you use, and how long the rice sits in that water. Basically, there are no studies yet that prove the NPK concentration in rice water.
How to make rice water for orchids: Recipe
There are basically two different ways you can make rice water for orchids.
The first is to soak the rice in water, just as you do to rinse it before cooking. The second way is to use double the amount of water and boil it with the rice for a few minutes and then strain the water. However, this second method takes too long.
So back to the first method, you need to rinse the rice in water and swish it around in it for a few minutes to clean the rice grains. What remains in the water is what you will use for your orchids.
There is another method, but it poses a great risk of root rot in orchids. It is fermented rice water. The recipe is the same, only the time when the rice is in the water in a shady, cool place is extended to 3-4 days. Some authors even talk about 10 days. This allows fungi to grow in the water and feed on the rice, turning the water into a fermented solution.
According to a 2021 study,(1)fermented rice water had higher nutrient concentrations (compared to non-fermented rice water), especially N, P, and K at 59.7, 60.2, and 25.0%, respectively, due to the presence of beneficial microorganisms such as Bacillus velezensis, Klebsiella pneumoniae, and a variety of Enterobacter spp. which are N-fixing and P- and K-solubilizing bacteria.
Rice water provides nutrients to the orchid’s mycorrhizal fungi.
It has long been known that orchids live in a symbiotic relationship with certain fungi called mycorrhiza. Mycorrhiza comes from the Greek: “mykos” means fungus and “riza” means roots. The fungus provides the roots with all the nutrients they cannot digest themselves. Rice water provides this fungus with a healthy amount of starch in the form of carbohydrates, which it eats.
In summary, the rice water provides the fungus in the orchid pot with the sugars and starches it needs and nourishes it. In turn, the fungus decomposes the elements in the potting soil and converts them into nutrients that can be easily absorbed by the orchid roots, which means that the orchid has to use less energy.
Rice water as a fertilizer for rapid growth
The breakdown of starch that rice water provides is for energy for your orchid. The fungi that receive this starchy water from the pre-rinsed rice increase the amount of CO2 in the orchid pot along with additional doses of nitrogen, phosphorus and potassium. This promotes their growth.
According to a study (2) by Dr. Christopher Teh (expert in plant modeling, environmental biophysics and soil conservation), lecturer at the Faculty of Agriculture, University Putra Malaysia, rice water contains nutrients that could supplement conventional fertilizers. It has been reported to increase the growth of many plants, from above-ground to below-ground biomass.
White or brown rice: which is better?
Few studies (2) compared the effects of white rice (WR) and brown rice (BR) water on plant growth. Purnami et al. (2014) evaluated the use of WR and BR water on the growth of Phalaenopsis orchids and found that using BR water once every four days increased root length, plant height, and biomass significantly more than WR water.
Can you replace your orchid fertilizer with rice water?
It is not recommended to completely replace the rice water with chemically produced fertilizer, because your orchid still needs other micronutrients that the rice water does not provide. It is good to set a schedule for when you fertilize your orchids and keep the dosage between the recommended levels. With rice water, we don’t know exactly what those dosages are. You could quickly overdose on a micronutrient. We recommend that you use rice water no more than once a month and maintain your normal fertilization schedule with the recommended NPK ratio of 20-2-20.
1. Agronomy 2021 ; Chemical and Microbial Characterization of Washed Rice Water Waste to Assess Its Potential as Plant Fertilizer and for Increasing Soil Health.
2. Pertanika j. Sci. & Technol (2021) ; Wastewater from Washed Rice Water as Plant Nutrient Source: Current Understanding and Knowledge Gaps.